Earplugs

ABSTRACT

There are disclosed earplugs composed of certain polymeric foam materials. The earplugs are of generally cylindrical shape and of somewhat larger diameter than the human ear canal. The earplugs are composed of a foamed plasticized polymeric material having a sufficiently high concentration of plasticizer to provide the earplug with a reduced rate of recovery from compression.

The present invention relates generally to earplug constructions andmore particularly to earplug constructions adapted for insertion intothe ear canal.

Many devices are known which are adapted for insertion into the humanear canal in order to suppress or attenuate the transmission ofdangerous noise and thus confer a measure of protection to theanatomical hearing apparatus. Such devices have taken many forms. Forinstance, perhaps the simplest earplug is formed of wadded cotton. Whileblessed with the benefit of simplicity, such earplugs are not normallygreatly effective as acoustic barriers. In another embodiment of thissimple earplug, a fibrous material, such as cotton wadding, isimpregnated with a compliant waxy substance. Yet another form of earplugis composed of a shapeless, compliant, "dead soft" mineral-filled waxysubstance. These ear-plugs are normally deficiant due to a lack ofsufficient resiliency; thus, when deformed or compressed in order toenter the ear canal such earplugs do not normally recover or expandsufficiently so as to effectively obturate the ear canal. Still otherearplugs are known which take the form of molded elastomeric structures,natural rubber being a common material of construction. Included withinthis class are earplugs having molded therein check valves and othersubstructures designed to allow normal voice tones to be transmittedtherethrough while cancelling or preventing transmission of injuriousoverpressures. Such molded elastomer earplugs suffer from the fact thattheir size and shape is preordained and fixed in the molding thereof.Thus, they must initially be carefully fitted to the wearer in order toprovide security, comfort and effective sound attenuation properties.Unfortunately, the size and shape of the human ear canal is quitevariable amongst persons; indeed, bilateral symmetry in a singleindividual is often lacking. Accordingly, it is not possible tomanufacture molded elastomeric earplugs of a universally useful size andshape.

In recent years there have come into extensive usage lightweightearphones or headphones comprising generally a miniature speaker havingtubular member(s) extending therefrom the tips of which members areadapted for insertion in the external auditory meatus. Said tips aregenerally comprised of a foamed or unfoamed polymeric material such asneoprene or sponge rubber. In the case of the unfoamed polymeric tipmembers major deficiencies usually reside in the facts that the tipmembers (1) tend to slip out of the ear canal, and (2) the relativelynon-compliant character of the polymeric material does not lend itselfto complete obturation of the ear canal. Thus, bothersome externalambient noise can often by-pass such unfoamed tip members. In the caseof sponge rubber tip members the resiliency of the sponge materials isgenerally excessively rapid and mitigates against actual insertion ofthe tip member into the ear canal proper. Such tip members are usuallyworn, therefore, in a manner such as to urge the respective membersinwardly against the external auditory meatus. This is often founduncomfortable and, in any case, is not ordinarily efficient in blockingthe ear canal.

In accordance with the present invention, however, there are providedearplug structures which substantially ameliorate or overcome theaforedescribed problems.

OBJECTS OF THE INVENTION

It is a principal object of the invention to provide novel earplugs.

It is another object of the invention to provide earplugs adapted forinsertion into the ear canals with substantially complete obturationthereof.

It is another object of the invention to provide earplugs havingexcellent sound barrier properties.

It is another object of the invention to provide earplugs adapted forinsertion into the ear canals wherein bone conduction of sound (such asthrough the plug and into the mastoid process) is substantiallycompletely avoided.

It is still another object of the invention to provide novel earinsertable earpieces for lightweight earphone devices.

Other objects and advantages of the invention will in part be obviousand will in part appear hereinafter.

GENERAL DESCRIPTION OF THE INVENTION

In accordance with the present invention there are provided earplugs ofgenerally cylindrical shape and of somewhat larger diameter than that ofthe human ear canal. Said earplugs are composed of a foamed polymericmaterial having a rate of recovery from 60 percent compression to 40percent compression thereof of from 1 to 60 seconds and an equilibriumpressure at 40 percent compression thereof of from 0.2 to 1.3 p.s.i.

THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of an earplug of theinvention.

FIG. 2 is a perspective, partially sectioned view of an earpiece portionof an earphone bearing a modified foamed polymeric earplug of theinvention as the external ear insertable tip member.

.Iadd.FIG. 3 is a perspective view of another embodiment of theinvention having a truncated cone shape. .Iaddend.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 it will be seen that the earplug of the invention isof generally cylindrical shape and has a diameter somewhat greater thanthat of the average adult human ear canal. For instance, a diameter ofbetween about 3/8 inch and about 3/4 inch is generally acceptable.Optimally, the diameter of the earplug will be between 9/16 inch and11/16 inch. Further, it should be noted and understood that the term"cylindrical" as employed herein includes within its scope structureshaving a relatively shallow truncated cone shape or a substantiallyspherical shape. Where the earplug takes the form of a truncated cone,the above diameter criteria may be employed taken at the midpoint of thecone. Where the earplug is spherical, the above criteria may be appliedto the diameter of said sphere.

The length of the earplug can generally be between about 1/2 inch toabout 1 inch. At lengths substantially greater than about 1 inch, forinstance, sufficient material can overhang the external ear so as to bebothersome to the wearer. Desirably, the length of the earplug will bebetween 7/16 and about 3/4 inch.

Any flexible polymeric material which can be foamed so as to result inan ultimately formed earplug structure meeting the recovery rate andpressure criteria set forth hereinabove constitutes a satisfactorymaterial of construction in the earplugs of the invention. Accordingly,polymers of ethylene, propylene, vinyl chloride, vinyl acetate,diisocyanate, cellulose acetate or isobutylene can all be generallyemployed. In particular, however, I much favor vinyl chloridehomopolymers and copolymers comprising at least 85 percent by weight ofvinyl chloride and up to 15 percent by weight of other monomers such asvinylidene chloride, vinyl esters of carboxylic acids, e.g., vinylacetate, vinyl propionate, vinyl butyrate and vinyl benzoate, esters ofunsaturated acids, e.g., alkyl acrylates such as methyl acrylate, ethylacrylate, propyl acrylate, butyl acrylate, allyl acrylate, and thecorresponding esters of methacrylic acid; vinyl aromatic compounds,e.g., styrene, ortho-chlorostyrene, para-chlorostyrene,2,5-dichlorostyrene, 2,4-dichlorostyrene, paraethylstyrene, vinylnaphthalene and α-methyl tyrene, dienes such as butadiene andchlorobutadiene, unsaturated amides such as acrylic acid amide andacrylic acid anilide; unsaturated nitriles such as acrylic acid nitrile;and esters of α,β-unsaturated carboxylic acids, e.g., the methyl, ethyl,propyl, butyl, amyl, hexyl, heptyl, octyl, allyl, methallyl, and phenylesters of maleic, crotonic and fumaric acids and the like. Such vinylchloride based polymers, and particularly the vinyl chloridehomopolymers, can normally be compounded into plastisol form with ablowing agent and a high concentration of a suitable organic plasticizerso as to result in stabilized foams having the rate of recovery andpressure characteristics necessary in the compositions from which theearplugs of the invention are fabricated.

With respect to said characteristics, it is clear that the relativelyslow recovery rate in returning from 60 percent compression to 40percent compression of the foamed materials employed in the earplugconstruction of the invention confers to the user the ability toinitially compress or otherwise deform the earplug and providesufficient time for insertion thereof into the ear canal. Subsequent tosaid insertion, the compressed or deformed earplug slowly recovers andattempts to regain its original shape. By so doing, the recoveringpolymeric material conforms to the structure of the ear canal andestablishes substantially complete obturation thereof. In a preferredembodiment of the invention, the recovery rate of the foamed polymercomposition will be between 2 and about 20 seconds.

The manner in which the recovery rate of the foamed polymer compositionis determined for the purposes of the present invention is as follows:

Plugs of the polymeric foam composition are cut with a hollow tubeborer, the dimensions of the plugs being about 0.630-0.640 inch indiameter and having a length of between 0.495 and 0.615 inch. A parallelplate gauge is employed having a spacing of 0.375 inch between theopposing plate surfaces. Said 0.375 inch spacing between plates thuscorresponds to about 40 percent compression of the original plugdiameter. A plug specimen is twirled lengthwise between the fingers for15 to 30 seconds with an ultimate compression of the plug to about 0.25inch in diameter, corresponding to about 60 percent reduction in theoriginal diameter thereof. The plug is then inserted lengthwise andreleased between the parallel plates, the time from said release tocontact of 75 percent of the linear surface of the plug with both platesbeing determined by stopwatch measurement. In order to maximize therelative precision of the test, a number of test specimens taken fromthe same sample foam are employed and the results averaged.

The 40 percent compression equilibrium pressure testing of the polymericfoam is accomplished employing the test plugs produced and employed inthe above recovery rate testing procedure. In pressure testing, however,there is employed an Instron Universal Testing Instrument, Model TTC,having a parallel plate specimen holder in which the parallel plates arespaced 0.375 inch apart. The Instron is further equipped with a 1 poundload cell. Test plugs of the foamed polymeric composition are fingertwirled in the manner described previously for a 30 second period andare placed lengthwise between the plates of the parallel specimenholder. When the load cell reading attains a 40 to 80 percent full scaledeflection, no further specimens are added. The instrument and specimensare allowed to stand for 10 minutes in order to attain substantialequilibrium and the number of plugs and the measured total pressure arerecorded. Since the contact area of each plug with the plates of thespecimen holder corresponds to about 0.25 in.², the average pressureexerted by each plug specimen is determined by the equation: ##EQU1##

The pressure criteria established hereinbefore for the foamed polymericcompositions employed in the fabrication of the earplugs of theinvention is also important in that the achievement of such pressurecharacteristics insures that the completed earplug will bear inobturating relationship against the ear canal but with insufficientpressure as to cause discomfort to the wearer. In a preferredembodiment, the foamed polymeric compositions employed in thefabrication of the earplugs of the invention will have a 40 percentcompression equilibrium pressure of between 0.35 and 1.0 p.s.i.

Taken together, the pressure and recovery rate criteria of the foamedpolymeric compositions also define a composition having the furthercharacteristic of relative "deadness." Thus, while form stable in thesense that the earplug, when deformed, will tend to recover its originalshape and size, the slow rate of recovery thereof and the very smalloverall pressure exerted by the plug surfaces on the constraining earcanal further insure the fact that little sound will be transmittedthrough the material and into the bony structure of the canal. This,too, is highly advantageous since substantial undesirable soundtransmission by way of bone conduction through the mastoid process canoccur with solid earplugs.

There follow a number of non-limiting illustrative Examples:

EXAMPLE 1

A vinyl chloride plastisol formulation was compounded employing thefollowing ingredients:

    ______________________________________                                                                   Parts                                                                         by                                                                            Weight                                             ______________________________________                                        Opalon 440, a general purpose homopolymer of vinyl                                                         115                                              chloride produced by Monsanto Co., St. Louis,                                 Missiouri                                                                     Admex 523, an aromatic polyester plasticizer                                                               95                                               produced by Archer-Daniels-Midland Co.,                                       Minneapolis, Minnesota                                                        Estynox 203, an epoxidized soya bean oil                                                                   5                                                stabilizer/plasticizer produced by The Baker Castor                           Oil Co., Bayonne, New Jersey                                                  Estynox 203, an epoxidized soya bean oil                                                                   5                                                stabilizer/plasticizer produced by The Baker Castor                           Oil Co., Bayonne, New Jersey                                                  Kempore 200, an azodicarbonamide foaming agent                                                             8                                                produced by National Polychemicals, Inc.                                      Wilmington, Massachusetts                                                     Antimony Trioxide flame retardant                                                                          8                                                Advastab T-150, organometallic stabilizer produced                                                         2                                                by Advance Division, Carlisle Chemical Works, Inc.,                           New Brunswick, New Jersey                                                     Houdry FS-100, a polymeric surfactant produced by                                                          2                                                Air Products and Chemicals, Inc., Philadelphia,                               Pennsylvania                                                                  Vanstay 8014, stabilizer produced by R.T.                                                                  3                                                Vanderbilt Co., Inc., New York, New York                                      ______________________________________                                    

The resulting plastisol was cast on release paper and doctor bladed to athickness of about 77 mils. The cast plastisol was continuouslyconducted through an oven heated to a nominal temperature of about 420°F at a nominal residence time of about 5 minutes. The resulting foamedsheet composition had a density of about 7 lbs/ft³, a rate of recoveryfrom 60 percent compression to 40 percent compression of about 4 secondsand a 40 percent compression equilibrium pressure of about 0.78 p.s.i.When examined under 75x magnification, the foamed polymer appeared to beof predominantly closed-celled structure.

When cut into cylindrical plugs of about 5/8 inch diameter by about 5/8inch length, the resulting structures could be finger compressed andinserted into the ear canals without difficulty. The compressed plugsthereafter recovered to substantially completely and comfortablyobturate the ear canals and were found to be highly effective inattenuating the transmission of 15-15,000 Hz/sec frequenciestherethrough.

Referring now to FIG. 2, several of the earplugs are coaxially boredthroughout their lengths with a central corer having a diameter of about1/8 inch. The resulting structures are then employed as a covering 3over tubular tip portion 5 of a lightweight headphone set (partiallyshown). Again, it is found that the foamed polymeric structures arecompressible to below the dimensions of the ear canal and can becomfortably inserted therein with subsequent slow recovery thereof tosubstantially completely fill the cross-section of the ear canal. Theheadphone set is adjudged to be superior in wearer comfort and is highlyeffective in selectively conducting sound only through the tubular soundconductor 7 thereof.

EXAMPLE 2

A foamable polyvinyl chloride plastisol composition was formulatedemploying the following ingredients:

    ______________________________________                                                                   Parts                                                                         by                                                                            Weight                                             ______________________________________                                        Opalon 440                   100                                              Admex 523                    95                                               Estynox 203                   5                                               Kempore 200                   4                                               Antimony trioxide flame retardant                                                                          10                                               Surfex MM, a precipitated calcium carbonate filler                            produced by Diamond Alkali Co., Cleveland, Ohio                                                            15                                               Advastab T-150                2                                               Houdry FS-100                 2                                               Vanstay 8014                  3                                               ______________________________________                                    

The resulting plastisol composition was cast on release paper and doctorbladed to a thickness of about 114 mils. The cast sheet was thencontinuously fed through an oven as in Example 1. The resulting foamedpolyvinylchloride sheet had a density of about 13 lbs/ft³, a rate ofrecovery from 60 percent compression to 40 percent compression of about1 second and a 40 percent compression equilibrium pressure of about1.32.

When cut into cylindrical structures of about 5/8 inch diameter and 5/8inch length, the resulting wares were found to be acceptable as earplugsand could be inserted into the ear canals. However, due principally tothe substantially more rapid recovery rate than the composition ofExample 1, the wearer was required to insert the plugs with considerablymore rapidity following compression thereof and certain of the testsubjects were aware of the pressure exerted by the plugs on the earcanal.

EXAMPLE 3

Two polyvinylchloride formulations having substantially similaringredients as employed in Examples 1 and 2 but different relativeconcentrations were produced. Upon testing, one of the resultingpolyvinylchloride foams had a density of about 4 lbs/ft³, a recoveryrate from 60 percent compression to 40 percent compression of about 106seconds and an exerted equilibrium pressure at 40 percent compression ofabout 0.19 p.s.i. Earplugs formed of this material were found to bedeficient in that the recovery rate was excessively slow and the exertedpressure upon the ear canal was slightly below that required tocompletely obturate the ear canal with the foamed polymeric shape. Theother foamed polyvinylchloride sheet composition was found to have anapparent density of about 6 lbs/ft³, a recovery rate (60 to 40 percentcompression) of about 13 seconds and an exerted equilibrium pressure at40 percent compression of about 0.37 p.s.i. Cylindrical (includingtruncated cone shapes) earplugs formed of this material were found to beof excellent quality in terms of facile insertion, wearer comfort andsound attenuation properties.

While there are above described a number of specific embodiments of thepresent invention, it is obviously possible to produce other embodimentsand various equivalent modifications thereof without departing from thespirit of the invention.

Having set forth the general nature and several preferred embodiments ofthe present invention, the true scope thereof is now particularlypointed out in the appended claims.

What is claimed is:
 1. An earplug of generally cylindrical shape havinga diameter of between 3/8 and 3/4 inch, a length .[.to.]. .Iadd.of.Iaddend.between 1/2 and 1 inch and composed of a resilient plasticisedpolymeric foam having a sufficiently high concentration of organicplasticizer therein as to provide said foam with a rate of recovery.[.of.]. .Iadd.from .Iaddend.60 percent compression thereof to 40percent compression .Iadd.thereof .Iaddend.of from 1 to 60 seconds andan equilibrium pressure .[.of.]. .Iadd.at .Iaddend.40 percentcompression thereof of from 0.2 to 1.3 p.s.i.
 2. The earplug of claim 1wherein said polymeric foam has a rate of recovery of from 2 to 20seconds.
 3. The earplug of claim 1 wherein said polymeric foam has anequilibrium pressure at 40 percent compression of between 0.35 and 1.0p.s.i.
 4. The earplug of claim 1 wherein the polymeric constituent ofsaid foam is a polymer of vinyl chloride.
 5. The earplug of claim 1wherein the polymeric constituent of said foam is a homopolymer of vinylchloride.
 6. The earplug of claim 1 having a diameter of between 9/16and 11/16 inch.
 7. The earplug of claim 1 having a length of between7/16 and 3/4 inch.
 8. The earplug of claim 1 wherein said polymeric foamis formed from a polyvinylchloride plastisol.
 9. The earplug of claim 1having a truncated cone shape.
 10. The earplug of claim 1 having asubstantially longitudinal bore therethrough said bore being adapted toreceive the tip portion of a sound conducting tube. .Iadd.
 11. Anearplug having a size and shape adapted to be compressed and insertedinto the human ear canal and there allowed to expand and obturate theear canal, said earplug comprising a resilient plasticized polymericfoam having a sufficiently high concentration of organic plasticizertherein as to provide said foam with a rate of recovery from 60 percentcompression thereof to 40 percent compression thereof of from 1 to 60seconds and an equilibrium pressure at 40 percent compression thereof offrom 0.2 to 1.3 p.s.i. .Iaddend..Iadd.
 12. An earplug as in claim 11having a generally cylindrical shape. .Iaddend..Iadd.
 13. An earplug asin claim 11 wherein said polymeric foam has a rate of recovery from 60percent compression thereof to 40 percent compression thereof from 2 to20 seconds. .Iaddend..Iadd.
 14. An earplug as in claim 11 wherein saidpolymeric foam has an equilibrium pressure at 40 percent compressionthereof from 0.35 to 1.0 p.s.i. .Iaddend..Iadd.
 15. An earplug as inclaim 11 wherein the polymeric constituent of said foam is a polymer ofvinyl chloride. .Iaddend..Iadd.
 16. An earplug as in claim 11 whereinsaid polymeric foam is formed from a polyvinylchloride plastisol..Iaddend..Iadd.
 17. An earplug as in claim 11 having a truncated conicalshape. .Iaddend..Iadd.
 18. An earplug as in claim 11 having a boretherethrough, said bore being adapted to receive a sound conductingtube. .Iaddend..Iadd.
 19. An earplug as in claim 18, further comprisinga sound conducting tube mounted in said bore. .Iaddend.